Department of Electronics & Communication

Engineering

LAB MANUAL

SUBJECT: ELECTRONICS LAB - II [04BEC202]

B.Tech II Year – IV Semester

(Branch: ECE)

BHAGWANT UNIVERSITY

SIKAR ROAD, AJMER

DEPARTMENT OF ECE

II YEAR IV SEMESTER ECE

LIST OF EXPERIMENTS

Course/Paper: 04BEC-202

BEC Semester-IV

1. Plot gain-frequency characteristics of BJT amplifier with and

without negative feedback in the emitter circuit and determine

bandwidths, gain bandwidth products and gains at 1kHz with and

without negative feedback.

2. Study of series and shunt voltage regulators and measurement of

line and load regulation and ripple factor.

3. Plot and study the characteristics of small signal amplifier using

FET.

4. Study Wein bridge oscillator and observe the effect of variation in

R & C on oscillator frequency

5. Study transistor phase shift oscillator and observe the effect of

variation in R & C on oscillator frequency and compare with

theoretical value.

6. Study the following oscillators and observe the effect of variation

of C on oscillator frequency: (a) Hartley (b) Colpitts

7. Design Fabrication and Testing of k-derived filters (LP/HP).

8. Study of a Digital Storage CRO and store a transient on it.

9. To plot the characteristics of UJT and UJT as relaxation.

10. To plot the characteristics of MOSFET and CMOS.

DC Supply

B Base

- VRC +

RC=1k

Collector

B

A

1M

C

RB=330k

Emitter

IB

EXPERIMENT 1: PLOT GAIN-FREQUENCY CHARACTERISTICS

OF BJT AMPLIFIER.

Objectives:

To graph the collector characteristics of a transistor using experimental

methods.

To measure AC and DC voltages in a common-emitter amplifier.

Equipment: Instruments

1 DC Power Supply

3 Digital Multimeter

(DMM) 1 Function

Generator

1 Oscilloscope

Components

Capacitors: 15 μF, 10 μF

Resistors: 1 k, 3 k, 10 k, 33 k, 330 k, 10 k

potentiometer, 1M potentiometer Transistors: 2N3904

Procedure:

Part A : The Collector Characteristics (BJT)*Using two potentiometers*

1. Construct the circuit of Fig. 4.1. Vary the 1M potentiometer to set IB

= 10

A as in Table 4.1.

20V

A

10k

C

Fig. 4.1

2. Set the VCE to 2V by varying the 10k potentiometer as required by

the first line of Table 4.1.

3. Record the VRC and VBE values in Table 4.1.

4. Vary the 10 k potentiometer to increase VCE from 2V to the values

appearing in Table 4.1. (Note: IB should be maintained at 10 A for

the range of VCE levels.) Record VRC and VBE values for each of the

measured VCE values. Use the mV range for VBE.

5. Repeat step 2 through 5 for all values of IB indicated in Table 4.1. 6. Compute the values of IC (from IC = VRC/RC) and IE (from IE = IB+IC).

Use measured resistor value for RC. 7. Using the data of Table 4.1, plot the collector characteristics of the

transistor on a graph paper. (Plot IC versus VCE for the various values of IB. Choose an appropriate scale for IC and label each IB curve).

Part B : Common-Emitter DC Bias

1. Measure all resistor values (R1, R2, RC and RE) from circuit in Fig. 4.2

using DMM.

2. Calculate DC Bias values (VB, VE, VC and IE) and record them.

3. Calculate AC dynamic resistance, re.

4. Construct circuit as of Fig. 4.2 and set VCC = 10 V.

5. Measure the DC bias values (VB, VE, VC and IE) and record them.

6. Calculate IE using values obtained in Step 5.

7. Calculate re using the value of IE from Step 6.

8. Compare value of re obtained both from Step 3 & 7.

Fig. 4.2

PSPICE Instructions:

Using PSPICE Simulation, find the DC Bias values (VB, VE, VC and IE) for the circuit in

Fig.

Compare the values obtained from PSPICE with the experimental ones.Results and Calculations:

DC Supply

Part A – Step 3

IB

(A)

VCE

(V)

meas

VRC

(V)

meas

IC

(mA)

(calc)

VBE

(V)

meas

IE

(mA)

(calc)

2

4

10 6

8

2

4

30 6

8

2

50 4

6

8

Table

4.1

Part B

R1 (measured) =_________ , R2 (measured) =__________ , RC

(measured)= ________________ RE(measured) = ____________

VB (calculated) = ______________-__, VE (calculated) = ________

VC (calculated) =_____________ , IE (calculated) = ____________

re (calculated) =

VB (measured) = __________, VE (measured) = ____________VC

(measured) = ,IE (calculated) using

measured values of VE and RE =

IE VE / RE

re (measured) = , using measured IE from Step 6.

Graph IC versus VCE for each value of IB (use graph paper)

RESULT : Thus we have observed gain-frequency characteristics of BJT

amplifier.

EXPERIMENT 2: STUDY OF SERIES AND SHUNT VOLTAGE

REGULATORS.

AIM: TO STUDY ABOUT SERIES AND SHUNT VOLTAGE REGULATORS.

THEORY: The regulated power supply is a combination of three circuits, the

bridge rectifier, the capacitor filter and zener diode voltage Regulator.

Basically there are two types of voltage regulators (i) Series Voltage

Regulator (ii)Shunt

Voltage Regulator

The series Regulator is placed in series with load and Shunt Regulator is placed

in parallel with Load.

TRANSISTOR SERIES VOLTAGE REGULATOR

A voltage Regulator generally employs some active devices such as zener,

or a transistor or both to achieve its objective. A series voltage regular using

a transistor and zener diode is as shown,

The circuit is called a series voltage regulator because the load current passes

through the series transistor Q1.The main drawback of series regulator is that

the pass transistor can be destroyed by excessive load current.

TRANSISTOR SHUNT VOLTAGE REGULATOR

An increase in input voltage results in increase in output voltage and base –

Emitter voltage.

RESULT : Thus we have studied about series and shunt voltage regulators..

EXPERIMENT 3: CHARACTERISTICS OF FIELD EFFECT

TRANSISTOR

AIM:

To obtain the Drain and Transfer (V-I) characteristics of

FET and to plot the characteristics.

APPARATUS REQUIRED:

S.NO.

NAME OF THE EQUIPMENT

TYPE

RANGE QUANTITY

(NO.S)

1 FET BFW10/11 1

2 Resistor 1 kΩ 2

3 Voltmeter D.C (0 – 5V)

(0 – 100V)

One from

each

4 Ammeter D.C (0 – 50mA) 1

5 Regulated Power Supply D.C (0 – 30V) 2

6 Bread Board 1

7 Connecting wires Required

THEORY:

A FET is a three terminal device, having the characteristics of

high input impedance and less noise, the Gate to Source junction of

the FET s always reverse biased. In response to small applied voltage

from drain to source, the n-type bar acts as sample resistor, and the

drain current increases linearly with VDS .With increase in ID the

ohmic voltage drop between the source and the channel region

reverse biases the junction and the conducting position of the

MODEL GRAPH:

Transfer Characteristics Drain Characteristics

VGS(V) Vs ID(mA) VDS(V) Vs ID(mA)

JFET PIN DIAGRAM

channel begins to remain constant. The VDS at this instant is called

“pinch of voltage”. If the gate to source voltage (VGS) is applied

in the direction to provide additional reverse bias, the pinch off

voltage ill is decreased.

PROCEDURE:

1. Identify the terminals of the FET given and set up the circuit on

breadboard as shown in figure.

2. Wire the circuit as shown in figure. By keeping the Gate Source voltage constant and varying the Drain Source voltage, ID

eadings are noted down.

3. Wire the circuit as shown in figure. By keeping the Drain Source

voltage constant and varying the Gate Source voltage, I

readings are noted down.

4. The above procedure was repeated and ammeter and voltmeter

readings were noted.

5. VI characteristics curves were drawn.

CIRCUIT DIAGRAM:

TABULATION:

Sl.No

VBB1 = VBB2 =

VE (V) IE (mA) VE (V) IE (mA)

1. 2.

3.

4.

5.

6.

7.

RESULT:

Thus the Drain and Transfer (V-I) characteristics of

the FET were obtained and the characteristics curves were

plotted.

EXPERIMENT 4: STUDY OF RC PHASE SHIFT OSCILLATOR.

AIM:

To design and set up an RC phase shift oscillator using BJT

and to observe the sinusoidal output waveform.

APPARATUS REQUIRED:

S.NO. NAME OF THE

EQUIPMENT

TYPE

RANGE QUANTITY

(NO.S)

1 Transistor BC547 1

2 Resistors 47kΩ, 10kΩ,2.2kΩ,680Ω

one from

each

3 Resistor 4.7kΩ 3

3 Capacitors 1µF,22µF one from

each

4 Capacitor 0.01 µF 3

5 CRO

6 RPS (0 – 30V) 1

7 Bread Board 1

8 Connecting wires

Required

THEORY: An oscillator is an electronic circuit for generating an AC signal

voltage with a DC supply as the only input requirement. The frequency

of the generated signal is decided by the circuit elements used. An

oscillator requires an amplifier, a frequency selective network and a

positive feedback from the output to the input.

The Barkhausen criterion for sustained oscillation is Aβ = 1 where

A is the gain of the amplifier and β is the feedback factor (gain).The

unity gain means signal is in phase. ( If the signal is 1800 out of phase

and gain will be -1). RC-Phase shift Oscillator has a CE amplifier

followed by three sections of RC phase shift feed-back Networks. The

output of the last stage is return to the input of the amplifier. The

values of R and C are chosen such that the phase shift of each RC

section is 60º.Thus The RC ladder network produces a total phase shift

of 180º between its input and output voltage for the given frequency.

Since CE Amplifier produces 180 º phases shift. The total phase shift

from the base of the transistor around the circuit and back to the base

will be exactly 360º or 0º. This satisfies the Barkhausen condition for

sustaining oscillations and total loop gain of this circuit is greater than

or equal to 1, this condition used to generate the sinusoidal

oscillations.

MODEL GRAPH:

BJT PIN DIAGRAM

CIRCUIT DIAGRAM:

PROCEDURE:

1. Identify the pin details of BC107 Transistor (or equivalent silicon

Transistor such as BC108/547) and test it using a millimeter. Set

up the circuit on breadboard as shown in figure.

2. A 12V Supply Voltage is given by using Regulated power supply

and output is taken from collector of the Transistor.

3. By using CRO the output time period and voltage are noted.

4. Plot all the readings curves on a single graph sheet.

RESULT:

Thus the RC phase shift oscillator using BJT was obtained and the

output waveform was plotted.

EXPERIMENT 5: STUDY OF WEIN BRIDGE OSCILLATOR.

AIM:

To design and set up a Wein Bridge oscillator using BJT and to

observe the sinusoidal output waveform.

APPARATUS REQUIRED:

S.NO. NAME OF THE

EQUIPMENT

TYPE

RANGE QUANTITY

(NO.S)

1 Transistor BC547 2

2 Resistors 47kΩ,

10kΩ,2.2kΩ,680Ω one from

each

3 Resistor 4.7kΩ 3

3 Capacitors 1µF,22µF one from

each

4 Capacitor 0.01 µF 3

5 CRO

6 RPS (0 – 30V) 1

7 Bread Board 1

8 Connecting wires

Required

THEORY: An oscillator is an electronic circuit for generating an AC signal

voltage with a DC supply as the only input requirement. The

frequency of the generated signal is decided by the circuit elements

used. An oscillator requires an amplifier, a frequency selective

network and a positive feedback from the output to the input.

The Barkhausen criterion for sustained oscillation is Aβ = 1 where A is

the gain of the amplifier and β is the feedback factor (gain).The unity

gain means signal is in phase. ( If the signal is 1800 out of phase and

gain will be -1).

A Wien bridge oscillator is a type of electronic oscillator that generates sine waves.

It can generate a large range of frequencies. The oscillator is based on a bridge

circuit originally developed by Max Wien in 1891 for the measurement of

impedances. The bridge comprises four resistors and two capacitors. The oscillator

can also be viewed as a positive gain amplifier combined with a bandpass filter that

provides positive feedback. Automatic gain control, intentional non-linearity and

incidental non-linearity limit the output amplitude in various implementations of the

oscillator.

The circuit shown to the right depicts a common implementation of the oscillator,

with automatic gain control, using modern components. Under the condition that

R1=R2=R and C1=C2=C, the frequency of oscillation is given by:

and the condition of stable oscillation is given by

CIRCUIT DIAGRAM:

MODEL GRAPH:

PROCEDURE:

1. Identify the pin details of BC107 Transistor (or equivalent silicon

Transistor such as BC108/547) and test it using a millimeter. Set

up the circuit on breadboard as shown in figure.

2. A 12V Supply Voltage is given by using Regulated power supply

and output is taken from collector of the Transistor.

3. By using CRO the output time period and voltage are noted.

4. Plot all the readings curves on a single graph sheet.

RESULT:

Thus the Wein Bridge oscillator using BJT was obtained and the

output waveform was plotted.

EXPERIMENT 6: STUDY OF COLPITTS OSCILLATOR.

AIM:

To design and set up a Colpitts oscillator using BJT and to

observe the sinusoidal output waveform.

APPARATUS REQUIRED:

S.NO APPARATUS SPECIFICATION QUANTITY

1. Transistor BC 107 1

2. Resistors 11.64 KΩ,

552.2Ω,10.02KΩ1.67kΩ

Each 1

3. Capacitors 53.5nF,80µF, 100mF 2,1,1

4. Inductor 0.78mH 1

5. RPS ±12V 1

6. CRO 1MHz 1

7. Connecting wires - Req.

THEORY:

A Colpitts oscillator is the electrical dual of a Hartley oscillator, where the feedback signal is taken

from an "inductive" voltage divider consisting of two coils in series (or a tapped coil). Fig. 1 shows the

common-base Colpitts circuit. L and the series combination of C1 and C2 form the parallel resonant tank

circuit which determines the frequency of the oscillator. The voltage across C2 is applied to the base-

emitter junction of the transistor, as feedback to create oscillations. Fig. 2 shows the common-collector

version. Here the voltage across C1 provides feedback. The frequency of oscillation is approximately

the resonant frequency of the LC circuit, which is the series combination of the two capacitors in

parallel with the inductor

DESIGN PROCEDURE:

Select a appropriate transistor and note down its specification such as VCE,IC(MAX), hfe(min) and

Vbe(sat).

VCC= VCEQ

R2=S* RE

VCC[R2/( R1+ R2)= VBE+VBE(SAT)

VR1+VR2=VCC

hfe ≥ C1* C2/( C1+ C1)

XCE ≤ RE/10

PROCEDURE:

Hook up the circuit as shown in the circuit diagram.

Switch on the power supply.

Slight modification in value of C1 and C2 can be made to get perfect sine wave output.

Observe the output waveform in CRO.

CIRCUIT DIAGRAM:

MODEL GRAPH:

TABULATION:

Amplitude(Volts) Time(ms) Frequency (KHz)

RESULT:

Thus the Colpitts oscillator was designed and its output waveform was verified.

EXPERIMENT 7: STUDY OF HARTLEY OSCILLATOR.

AIM:

To design and set up a Hartley oscillator using BJT and to

observe the sinusoidal output waveform.

APPARATUS REQUIRED:

S.NO APPARATUS SPECIFICATION QUANTITY

1. Transistor BC 107 1

2. Resistors 2.74 KΩ,

1.76KΩ,10.58KΩ

1,2,1

3. Capacitors 0.1µF, 0.1µF Each 2

4. Inductor 0.1mH,0.33mH Each 1

5. RPS ±12V 1

6. CRO 1MHz 1

7. Connecting wires - Req.

THEORY:

The Hartley oscillator is an electronic oscillator circuit in which the oscillation frequency is

determined by a tuned circuit consisting of capacitors and inductors, that is, an LC oscillator. The

Hartley oscillator is distinguished by a tank circuit consisting of two series-connected coils (or,

often, a tapped coil) in parallel with a capacitor, with an amplifier between the relatively high

impedance across the entire LC tank and the relatively low voltage/high current point between the

coils. The Hartley oscillator is the dual of the Colpitts oscillator which uses a voltage divider made

of two capacitors rather than two inductors. Although there is no requirement for there to be

mutual coupling between the two coil segments, the circuit is usually implemented using a tapped

coil, with the feedback taken from the tap, as shown here. The optimal tapping point (or ratio of

coil inductances) depends on the amplifying device used, which may be a bipolar junction

transistor.

DESIGN PROCEDURE:

Select a appropriate transistor and note down its specification such as VCE,IC(MAX), hfe(max) and

Vbe(sat).

VCC= VCEQ+ ICQ(RC+RE)

R2=S* RE

VCC[R2/( R1+ R2)= VBE+VBE(SAT)

VR1+VR2=VCC

PROCEDURE:

Hook up the circuit as shown in the circuit diagram.

Switch on the power supply.

Slight modification in value of L1 and L2 can be made to get perfect sinewave output.

Observe the output waveform in CRO.

CIRCUIT DIAGRAM:

MODEL GRAPH:

TABULATION:

Amplitude(Volts) Time(ms) Frequency (KHz)

RESULT:

Thus the Hartley oscillator was designed and its output waveform was verified.

EXPERIMENT 8: Characteristics of UJT and UJT as relaxation.

AIM:

To study and observe the characteristics of UJT.

APPARATUS:

Regulated power supply (0-30V) -2Nos

0-20V (DMM) -2Nos

mA (DMM) -1No.

Resistors 1Kohm -2Nos

Resistor 470 ohm -1No.

Breadboard Connecting wires

THEORY: A Unijunction Transistor (UJT) is an electronic semiconductor device that has only one

junction. The UJT Unijunction Transistor (UJT) has three terminals an emitter (E) and two bases

(B1 and B2). The base is formed by lightly doped n-type bar of silicon. Two ohmic contacts B1 and

B2 are attached at its ends. The emitter is of p- type and it is heavily doped. The resistance between

B1 and B2, when the emitter is open-circuit is called interbase resistance. The original Unijunction

transistor, or UJT, is a simple device that is essentially a bar of N type semiconductor material into

which P type material has been diffused somewhere along its length. The 2N2646 is the most

commonly used version of the UJT.

The UJT is biased with a positive voltage between the two bases. This causes a potential drop along

the length of the device. When the emitter voltage is driven approximately one diode voltage above

the voltage at the point where the P diffusion (emitter) is, current will begin to flow from the emitter

into the base region. Because the base region is very lightly doped, the additional current (actually

charges in the base region) causes (conductivity modulation) which reduces the resistance of the

portion of the base between the emitter junction and the B2 terminal. This reduction in resistance

means that the emitter junction is more forward biased, and so even more current is injected.

Overall, the effect is a negative resistance at the emitter terminal. This is what makes the UJT

useful, especially in simple oscillator circuits. hen the emitter voltage reaches Vp, the current starts o

increase and the emitter voltage starts to decrease. This is represented by negative slope of the

characteristics which is referred to as the negative resistance region, beyond the valley point, RB1

reaches minimum value and this region, VEB proportional to IE.

CIRCUIT DIAGRAM:

PROCEDURE:

1. Connection is made as per circuit diagram.

2. Output voltage is fixed at a constant level and by varying input voltage corresponding emitter

current values are noted down.

3. This procedure is repeated for different values of output voltages.

4. All the readings are tabulated and Intrinsic Stand-Off ratio is calculated using η = (Vp-

VD) / VBB

5. A graph is plotted between VEE and IE for different values of VBE.

OBSEVATIONS:

VBB=10 VBB=5 VBB=2

VEB(V) IE(mA) VEB(V) IE(mA) VEB(V) IE(mA)

RESULT: Thus we have studied and observed the characteristics of UJT.

EXPERIMENT 9: TO STUDY ABOUT CATHODE RAY OSCILLOSCOPE.

AIM:

To study about cathode ray oscilloscope (CRO).

APPARATUS:

CRO, CONNECTING LEADS, POWER SUPPLY.

THEORY:

An oscilloscope is a test instrument which allows us to look at the 'shape' of electrical signals by

displaying a graph of voltage against time on its screen. It is like a voltmeter with the valuable

extra function of showing how the voltage varies with time. A graticule with a 1cm grid

enables us to take measurements of voltage and time from the screen.

The cathode-ray oscilloscope (CRO) is a common laboratory instrument that provides accurate

time and amplitude measurements of voltage signals over a wide range of frequencies. Its

reliability, stability, and ease of operation make it suitable as a general purpose laboratory

instrument. The heart of the CRO is a cathode-ray tube.

The graph, usually called the trace, is drawn by a beam of electrons striking the phosphor coating

of the screen making it emit light, usually green or blue. This is similar to the way a

television picture is produced.

Oscilloscopes contain a vacuum tube with a cathode (negative electrode) at one end to emit

electrons and an anode (positive electrode) to accelerate them so they move rapidly down the

tube to the screen. This arrangement is called an electron gun. The tube also contains

electrodes to deflect the electron beam up/down and left/right.

The electrons are called cathode rays because they are emitted by the cathode and this gives the

oscilloscope its full name of cathode ray oscilloscope or CRO.

A dual trace oscilloscope can display two traces on the screen, allowing us to easily compare the

input and output of an amplifier for example. It is well worth paying the modest extra cost to

have this facility.

Setting up an oscilloscope: Oscilloscopes are complex instruments with many controls and they require some care to set

up and use successfully. It is quite easy to 'lose' the trace off the screen if controls are set

wrongly.

There is some variation in the arrangement and labeling of the many controls. So,

the following instructions may be adapted for this instrument.

1. Switch on the oscilloscope to warm up (it takes a minute or two).

2. Do not connect the input lead at this stage.

3. Set the AC/GND/DC switch (by the Y INPUT) to DC.

4. Set the SWP/X-Y switch to SWP (sweep).

5. Set Trigger Level to AUTO.

6. Set Trigger Source to INT (internal, the y input).

7. Set the Y AMPLIFIER to 5V/cm (a moderate value).

8. Set the TIMEBASE to 10ms/cm (a moderate speed).

9. Turn the time base VARIABLE control to 1 or CAL.

10. Adjust Y SHIFT (up/down) and X SHIFT (left/right) to give a trace across the middle

of the screen, like the picture.

11. Adjust INTENSITY (brightness) and FOCUS to give a bright, sharp trace.

The following type of trace is observed on CRO after setting up, when there is no input signal

connected.

FIG. OSCILLOSCOPR PROBES AND LEADS

Measuring voltage and time period

The trace on an oscilloscope screen is a graph of voltage against time. The shape of this graph is

determined by the nature of the input signal. In addition to the properties labeled on the graph, there is

frequency which is the number of cycles per second. The diagram shows a sine wave but these

properties apply to any signal with a constant shape

Amplitude is the maximum voltage reached by the signal. It is measured in volts.

Peak voltage is another name for amplitude.

Peak-peak voltage is twice the peak voltage (amplitude). When reading an

oscilloscope trace it is usual to measure peak-peak voltage.

Time period is the time taken for the signal to complete one cycle.

It is measured in seconds (s), but time periods tend to be short so milliseconds (ms) and

microseconds (µs) are often used. 1ms = 0.001s and 1µs = 0.000001s.

Frequency is the number of cycles per second. It is measured in hertz (Hz), but frequencies

tend to be high so kilohertz (kHz) and megahertz (MHz) are often used. 1kHz = 1000Hz and

1MHz = 1000000Hz.

Frequency = 1 Time period

Time period = 1 Frequency

A) Voltage: Voltage is shown on the vertical y-axis and the scale is determined by the Y

AMPLIFIER (VOLTS/CM) control. Usually peak-peak voltage is measured because it can be

read correctly even if the position of 0V is not known. The amplitude is half the peak-peak

voltage.

Voltage = distance in cm × volts/cm

B) Time period: Time is shown on the horizontal x-axis and the scale is determined by the

TIMEBASE (TIME/CM) control. The time period (often just called period) is the time for one cycle

of the signal. The frequency is the number of cycles per second, frequency = 1/time period.

Time = distance in cm × time/cm

RESULT: Thus we have studied about CRO.